In recent years, there has been a tremendous increase in interest in advanced safety features in automobiles. This has led to the development of advanced vehicle chassis control systems such as anti-lock brakes (ABS), traction control (TC), four wheel steer (4WS), electronic stability program (ESP), etc. Yaw rate is an important element of the vehicle dynamics that influences the driver's (and passenger's) perception of vehicle handling and safety features. Hence, a considerable level of effort is being directed towards developing reliable and accurate methods to monitor and control the yaw rate of an automobile.
Referring to the vehicle schematic shown in FIG. 1, the vehicle heading angle .psi.(t), is defined as the angle between the inertial X-axis (of the inertial X-Y-Z coordinate frame) and the body fixed x-axis (of the vehicle-fixed x-y-z coordinate frame). The time rate of change of .psi.(t), with respect to the vehicle-fixed coordinate system x-y-z, is the yaw rate, r(t). It is necessary to measure the vehicle yaw rate in various vehicle control applications, such as brake-steer, lateral dynamics control and safety warning systems such as collision warning and roadway departure warning systems. In order to measure the yaw rate, sensors are commercially available for use in vehicle control research. Currently, these sensors cost several hundred dollars each even in mass production quantities. This cost is extremely prohibitive for use in mass produced automobiles. Although it is expected that the cost of such sensors will be dramatically reduced in the future, it is of interest to consider methods to estimate the yaw rate accurately for near term use in vehicles.
The problem of estimating the yaw rate from vehicle acceleration measurements has already been considered (see U.S. Pat. No. 5,247,466). However, the approaches to date for yaw rate measurement using accelerometers have been based purely upon vehicle kinematics. Consequently, these methods are inherently sensitive to measurement noise.